下载文件时如何计算下载速度和估计剩余时间

Question

我通过requests下载文件：

import base64
import random

WORDLIST_LINKS = [
    'aHR0cHM6Ly9naXN0LmdpdGh1YnVzZXJjb250ZW50LmNvbS9Fa3VsdGVrL2FhODgyMDk5ZWQxYzNlZjAwNWYzYWY2ZjhmYmFhZTExL3Jhdy84ODQ4NjBhNjAzZWQ0MjE3MTgyN2E1MmE3M2VjNzAzMjNhOGExZWY5L2dpc3RmaWxlMS50eHQ=',
    'aHR0cHM6Ly9naXN0LmdpdGh1YnVzZXJjb250ZW50LmNvbS9Fa3VsdGVrL2JmM2MwYjQwMTVlYzlkMzY4YzBlNTczNzQ0MTAzYmU1L3Jhdy9lNzBhMThmOTUwNGYwZmMyYjRhMWRmN2M0Mjg2YjcyOWUyMzQ5ODljL29wZW53YWxsXzIudHh0',
    'aHR0cHM6Ly9naXN0LmdpdGh1YnVzZXJjb250ZW50LmNvbS9Fa3VsdGVrLzQ1ZTExZDBhMzNjZGE1YjM3NDM5OGYyMDgxYjEwZWZiL3Jhdy8wNzQ1ZGMzNjFlZDU5NjJiMjNkYjUxM2FkOWQyOTNlODk0YjI0YTY0L2RjLnR4dA==',
    'aHR0cHM6Ly9naXN0LmdpdGh1YnVzZXJjb250ZW50LmNvbS9Fa3VsdGVrLzNmMzcxMWUzMDdlOGM0ZTM0MDkzYzI1OGFkN2UzZWZkL3Jhdy9hMjNiYmM3YTgxNTZhOGU5NTU3NmViYTA3MmIwZDg4ZTJmYjk1MzZiL2dtYWlsXzIudHh0',
]
def download_rand_wordlist(b64link=random.choice(WORDLIST_LINKS)):
    """
      Download a random wordlist from some wordslits I have laying around

      > :param b64link: a base64 encoded wordlist link
    """
    filename = random_salt_generator(use_string=True)[0]
    print("Beginning download..")
    with open("wordlist.txt", "a+") as wordlist:
        response = requests.get(base64.b64decode(b64link), stream=True)
        total_length = response.headers.get('content-length')
        if total_length is None:
            wordlist.write(response.content)
        else:
            start = time.time()
            downloaded = 0
            total_length = int(total_length)
            for data in response.iter_content(chunk_size=1024):
                downloaded += len(data)
                wordlist.write(data)
                done = int(50 * downloaded / total_length)
                sys.stdout.write("\r[\033[93m{}\033[0m{}]".format("=" * done, " " * (50-done)))
                sys.stdout.flush()
    print("")
    print("Download complete, saved under: {}.txt. Time elapsed: {}s".format(filename, time.time() - start))

如何使用上面的代码计算下载速度和下载的估计剩余时间？